[R] Subsetting by a logical condition and NA's
Yuelin Li
yuelin at mail.med.upenn.edu
Tue Apr 23 06:24:21 CEST 2002
Hi, John,
Often I use y[ which(x == 5) ] to bypass the NAs, and
y[ -which(x == 5) ] includes the mismatches and NAs. In
all cases I have tested it works on both R and Splus,
which I think is worth the extra which(). Also
I think "x %in% c(5)" or match(x, table=5) in R gives you
what you wanted.
Yuelin.
----- On Mon, 22 Apr 2002, John Miyamoto wrote:
I have run into a general problem with subsetting of which the following
is a simple example. Suppose that
x <- c(5, NA, 7, 5, NA, 3)
y <- c(1, 2, 3, 4, 5, 6)
I want to extract the values of y for which x = 5, but y[x==5] yields
> y[x==5]
[1] 1 NA 4 NA
I find that y[!is.na(x) & x==5] yields the desired result:
> y[!is.na(x) & x==5]
[1] 1 4
but I am wondering whether there is a general way to specify a logical
condition such that it yields TRUE when the condition is true and FALSE
when the condition is either false or the input data is NA? For example,
is there a simpler way to produce the same results as y[!is.na(x) & x==5]?
John
--------------------------------------------------------------------
John Miyamoto, Dept. of Psychology, Box 351525
University of Washington, Seattle, WA 98195-1525
Phone 206-543-0805, Fax 206-685-3157, Email jmiyamot at u.washington.edu
Homepage http://faculty.washington.edu/jmiyamot/
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